This invention relates to an air heater arrangement for a clothes dryer which is an improvement over the type of arrangement disclosed in U.S. Pat. No 3,504,444. Heaters suitable for supplying a stream of heated air for use in such appliances are well known. They are usually composed of a blower of either the propeller fan or the squirrel cage type operating in conjunction with a heating element.
The heating element is mounted either upstream or downstream of the blower.
When a centrifugal squirrel cage type fan is utilized the heating element is usually mounted downstream of the exit from the blower in a duct adjacent to the blower. This type of arrangement is so well known that it is normally only diagrammatically shown in patents dealing with clothes dryers or other similar appliances. This can be seen, for example, in U.S. Pat. No. 2,498,478 to Balph; U.S. Pat. No. 2,863,224 to Zehrbach; U.S. Pat. No. 2,817,501 to Schubert; U.S. Pat. No. 2,815,416 to Kumler; and U.S. Pat. No. 2,654,961 to Manecke.
When a propeller fan type blower is utilized, the heating element is normally mounted in a duct located either upstream or downstream of the blower. When mounted downstream of the blower, the heating element usually takes the form of an array of electrical resistance wires disposed across the opening in the duct. This type of arrangement is shown, for example, in U.S. Pat. No. 2,942,353 to Barnett; U.S. Pat. No. 1,755,539 to Gerosa; U.S. Pat. No. 2,328,256 to Breckenbridge; U.S. Pat. No. 2,026,189 to Purkett; U.S. Pat. No. 2,617,203 to Murray; U.S. Pat. No. 2,708,230 to Bowman; and U.S. Pat. No. 2,679,112 to Thompson, which show a propeller type fan directing air directly over an electrical element, which element is mounted substantially in the same chamber as the fan.
An upstream heater configuration utilizing a propeller fan is shown in U.S. Pat. No. 2,587,646 to O'Neil, wherein an annular heating element is shown mounted upstream of a propeller type blower. Air is caused to be drawn over the heating elements as a result of the placement of a baffle behind the fan blade. Thereafter, the air passes over the propeller blade and is forced into the drying chamber through a perforated wall.
A disadvantage which occurs to a greater or lesser extent in the prior art heater arrangements discussed above is that air flow is diffused when it flows over the heating element. That is, with a downstream mounted heating element, the air leaving the blower travels to, and is spread across, the area of the full opening of the outlet of the blower or the duct in which the heating element is mounted. Thus the heating element "sees" a somewhat spread out air flow. Similarly, the air drawn over an upstream mounted heating element is somewhat diffused in terms of flow rate.
Because the velocity and volume of air flowing directly over the heating elements are somewhat diffused, as discussed above, it has been necessary to utilize higher gauge and therefore more expensive resistance elements, that is elements capable of withstanding higher temperatures than would be necessary for the same heat dissipation rate (and blower) if a less diffuse air flow were produced over the heating elements.
A second disadvantage of most prior art arrangements is the use of a separate structure for holding the heating element from that in which the fan operates. This requires additional cost factors in the manufacture of the appliance.